JPS6219102Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved switching regulator with multiple outputs.

As shown in Figure 1, the switching regulator converts commercial AC power directly into DC using a rectifying and smoothing circuit 1, and generates a high frequency signal from an oscillating circuit 2, such as 20KHz to
The switching transistor 3 is switched with a 50KHz pulse, and a voltage stabilized by the ferrite transformer 4, which is the collector load of the switching transistor 3, is obtained from the secondary side. Such a switching regulator can replace the conventional low frequency transformer with a small and lightweight high frequency transformer 4,
This greatly contributes to making power supplies smaller and lighter.

In the switching regulator mentioned above,
In order to stabilize the secondary side, fluctuations in the rectified DC stabilizing voltage on the secondary side are detected by an error amplifier 5,
A feedback control system is provided which applies this output to a pulse width modulation circuit 6 to modulate the pulse width of the high frequency reference pulse from the pulse oscillation circuit 2 and apply it to the switching transistor 3.

On the other hand, in a system where a logic circuit, which is a microcomputer-applied product, and mechanical parts such as relays or motors coexist, there are two power supplies: a high-precision +5V power supply for the logic circuit and a rough-precision +12V (or +24V) power supply for the mechanical system. Grid power is required. To configure this power supply with a switching regulator, the first
As shown in the figure, it is economical to provide the above-mentioned feedback control system for stabilization only on the +5V power supply, and not to provide the feedback control system for stabilization on the +12V power supply.

However, in such a configuration, even if the +12V power supply has no load or a light load, the switching transistor 3 is switched with a constant pulse width if a certain load is applied to the +5V power supply. For this reason +
There was a risk that the voltage of the 12V power supply would rise rapidly, exceeding the withstand voltage of the smoothing circuit capacitor or exceeding the allowable voltage range of the load.

In order to counter this drawback, as shown in Figure 1, +
A bleeder resistor 7 was connected between 12V and the common potential as a dummy load. Therefore, an invalid current was allowed to flow through the bleeder resistor 7 until it reached a level at which a +12V power supply could be stably obtained. Therefore, if a current of 100 mA is applied to the bleeder resistor 7, 12×
This resulted in a power loss of 0.1 = 1.2W, reducing the efficiency of the entire switching regulator.

The present invention has been made in view of this point, and one embodiment of the present invention will be described in detail below with reference to FIG. 2. Since the circuit of the present invention is almost the same as that shown in FIG. 1, the same parts as those shown in FIG. 1 are given the same figure number.

The most distinctive feature of the present invention is the connection of the bleeder resistor 10. In other words, the bleeder resistor 10 is +12V and +
The purpose is to connect between the 5V output terminals. According to such a configuration, even if a current of 100 mA is passed through the bleeder resistor 10, the power consumption is suppressed to (12-5)×0.1=0.7W, and the heat generation of the bleeder resistor 10 can be significantly reduced. Furthermore, the current flowing through the bleeder resistor 10 is +5V
Since it is consumed as load current of the power supply, it does not become reactive power.

As detailed above, according to the present invention, reactive power can be significantly reduced by changing the way in which the bleeder resistor 10 is connected, which is advantageous in that it can contribute to improving the efficiency of the switching regulator.

[Brief description of the drawings]

FIG. 1 is a circuit diagram explaining a conventional example, and FIG. 2 is a circuit diagram explaining the present invention. 1 is a rectifier and smoothing circuit, 2 is a pulse oscillation circuit, 3 is a switching transistor, 4 is a transformer, 5 is an error amplifier, 6 is a pulse width modulation circuit, and 10 is a bleeder resistor.

Claims (1)

[Scope of utility model registration request] It comprises a rectifying and smoothing circuit, a transformer, a switching element, and a control circuit connected to an AC power source, and a high frequency control pulse outputted from the control circuit is applied to the switching element to form a high frequency AC voltage, and the high frequency AC voltage is applied to the switching element. In a switching regulator that is applied to the primary side of a transformer to obtain a plurality of stabilized power sources on the secondary side, voltage fluctuations in the output of one of the transformers are detected to modulate the pulse width of the high frequency control pulse. A switching regulator having multiple outputs, characterized in that a bleeder resistor is connected between the first output and another output having a higher voltage than the first output.